PURPOSE: To improve the controlling performance of light-shielding in a greenhouse and to facilitate the light-shielding operation by detecting the condition of the internal and external environment of a greenhouse, inputting the detected data into an arithmetic and control unit, comparing the date with prescribed value and controlling the light-shielding property of a liquid crystal attached to the roof of the greenhouse.

CONSTITUTION: The growth condition of a raising seedling bed 13 is inputted into a CPU 8 and the detection data transmitted from an actinometer 9, a thermometer 10, a hygrometer 11 and a CO2 concentration meter 12 are also inputted into the CPU 8. The measured environmental conditions are compared with the prescribed environmental conditions by the CPU 8 and a prescribed voltage is outputted to a liquid crystal panel 2. The turbidity of the liquid crystal panel 2 can be varied by the applied voltage.